Overexpression of corticotropin-releasing factor receptor type 2 in the bed nucleus of stria terminalis improves posttraumatic stress disorder-like symptoms in a model of incubation of fear

Corticotropin-releasing factor signaling and its potential role in the prefrontal cortex-dependent regulation of anxiety

A large body of literature has highlighted the significance of the corticotropin-releasing factor (CRF) system in the regulation of neuropsychiatric diseases. Anxiety disorders are among the most common neuropsychiatric disorders. An increasing number of studies have demonstrated that the CRF family mediates and regulates the development and maintenance of anxiety. Thus, the CRF family is considered to be a potential target for the treatment of anxiety disorders. The prefrontal cortex (PFC) plays a role in the occurrence and development of anxiety, and both CRF and CRF-R1 are widely expressed in the PFC. This paper begins by reviewing CRF-related signaling pathways and their different roles in anxiety and related processes. Then, the role of the CRF system in other neuropsychiatric diseases is reviewed and the potential role of PFC CRF signaling in the regulation of anxiety disorders is discussed. Although other signaling pathways are potentially involved in the process of anxiety, CRF in the PFC primarily modulates anxiety disorders through the activation of corticotropin-releasing factor type1 receptors (CRF-R1) and the excitation of the cAMP/PKA signaling pathway. Moreover, the main signaling pathways of CRF involved in sex differentiation in the PFC appear to be different. In summary, this review suggests that the CRF system in the PFC plays a critical role in the occurrence of anxiety. Thus, CRF signaling is of great significance as a potential target for the treatment of stress-related disorders in the future.

Glutamatergic and GABAergic anteroventral BNST projections to PVN CRH neurons regulate maternal separation-induced visceral pain

Early-life stress (ELS) is thought to cause the development of visceral pain disorders. While some individuals are vulnerable to visceral pain, others are resilient, but the intrinsic circuit and molecular mechanisms involved remain largely unclear. Herein, we demonstrate that inbred mice subjected to maternal separation (MS) could be separated into susceptible and resilient subpopulations by visceral hypersensitivity evaluation. Through a combination of chemogenetics, optogenetics, fiber photometry, molecular and electrophysiological approaches, we discovered that susceptible mice presented activation of glutamatergic projections or inhibition of GABAergic projections from the anteroventral bed nucleus of the stria terminalis (avBNST) to paraventricular nucleus (PVN) corticotropin-releasing hormone (CRH) neurons. However, resilience develops as a behavioral adaptation partially due to restoration of PVN SK2 channel expression and function. Our findings suggest that PVN CRH neurons are dually regulated by functionally opposing avBNST neurons and that this circuit may be the basis for neurobiological vulnerability to visceral pain.

Reduction of DNMT3a and RORA in the nucleus accumbens plays a causal role in post-traumatic stress disorder-like behavior: reversal by combinatorial epigenetic therapy

Post-traumatic stress disorder (PTSD) is an incapacitating trauma-related disorder, with no reliable therapy. Although PTSD has been associated with epigenetic alterations in peripheral white blood cells, it is unknown where such changes occur in the brain, and whether they play a causal role in PTSD. Using an animal PTSD model, we show distinct DNA methylation profiles of PTSD susceptibility in the nucleus accumbens (NAc). Data analysis revealed overall hypomethylation of different genomic CG sites in susceptible animals. This was correlated with the reduction in expression levels of the DNA methyltransferase, DNMT3a. Since epigenetic changes in diseases involve different gene pathways, rather than single candidate genes, we next searched for pathways that may be involved in PTSD. Analysis of differentially methylated sites identified enrichment in the RAR activation and LXR/RXR activation pathways that regulate Retinoic Acid Receptor (RAR) Related Orphan Receptor A (RORA) activation. Intra-NAc injection of a lentiviral vector expressing either RORA or DNMT3a reversed PTSD-like behaviors while knockdown of RORA and DNMT3a increased PTSD-like behaviors. To translate our results into a potential pharmacological therapeutic strategy, we tested the effect of systemic treatment with the global methyl donor S-adenosyl methionine (SAM), for supplementing DNA methylation, or retinoic acid, for activating RORA downstream pathways. We found that combined treatment with the methyl donor SAM and retinoic acid reversed PTSD-like behaviors. Thus, our data point to a novel approach to the treatment of PTSD, which is potentially translatable to humans.

Acute Corticotropin-Releasing Factor Receptor Type 2 Agonism Results in Sustained Symptom Improvement in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Background

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex multi-symptom disease with widespread evidence of disrupted systems. The authors hypothesize that it is caused by the upregulation of the corticotropin-releasing factor receptor type 2 (CRFR2) in the raphé nuclei and limbic system, which impairs the ability to maintain homeostasis. The authors propose utilizing agonist-mediated receptor endocytosis to downregulate CRFR2.

Materials and Methods

This open-label trial tested the safety, tolerability and efficacy of an acute dose of CT38s (a short-lived, CRFR2-selective agonist, with no known off-target activity) in 14 ME/CFS patients. CT38s was subcutaneously-infused at one of four dose-levels (i.e., infusion rates of 0.01, 0.03, 0.06, and 0.20 μg/kg/h), for a maximum of 10.5 h. Effect was measured as the pre-/post-treatment change in the mean 28-day total daily symptom score (TDSS), which aggregated 13 individual patient-reported symptoms.

Results

ME/CFS patients were significantly more sensitive to the transient hemodynamic effects of CRFR2 stimulation than healthy subjects in a prior trial, supporting the hypothesized CRFR2 upregulation. Adverse events were generally mild, resolved without intervention, and difficult to distinguish from ME/CFS symptoms, supporting a CRFR2 role in the disease. The acute dose of CT38s was associated with an improvement in mean TDSS that was sustained (over at least 28 days post-treatment) and correlated with both total exposure and pre-treatment symptom severity. At an infusion rate of 0.03 μg/kg/h, mean TDSS improved by -7.5 ± 1.9 (or -25.7%, p = 0.009), with all monitored symptoms improving.

Conclusion

The trial supports the hypothesis that CRFR2 is upregulated in ME/CFS, and that acute CRFR2 agonism may be a viable treatment approach warranting further study.

Clinical Trial Registration

ClinicalTrials.gov, identifier NCT03613129.

The brain oxytocin and corticotropin-releasing factor systems in grieving mothers: What we know and what we need to learn

The bond between a mother and her child is the strongest bond in nature. Consequently, the loss of a child is one of the most stressful and traumatic life events that causes Prolonged Grief Disorder in up to 94 % of bereaved parents. While both parents are affected, mothers are of higher risk to develop mental health complications; yet, very little research has been done to understand the impact of the loss of a child, stillbirth and pregnancy loss on key neurobiological systems. The emotional impact of losing a child, e.g., Prolonged Grief Disorder, is likely accompanied by dysregulations in neural systems important for mental health. Among those are the neuropeptides contributing to attachment and stress processing. In this review, we present evidence for the involvement of the brain oxytocin (OXT) and corticotropin-releasing factor (CRF) systems, which both play a role in maternal behavior and the stress response, in the neurobiology of grief in mothers from a behavioral and molecular point of view. We will draw conclusions from reviewing relevant animal and human studies. However, the paucity of research on the tragic end to an integral bond in a female's life calls for the need and responsibility to conduct further studies on mothers experiencing the loss of a child both in the clinic and in appropriate animal models.

Both CRF1 and CRF2 receptors in the bed nucleus of stria terminalis are involved in baroreflex impairment evoked by chronic stress in rats

Chronic exposure to adverse events has been proposed as a prominent factor involved in etiology and progression of cardiovascular dysfunctions in humans and animals. However, the neurobiological mechanisms involved are still poorly understood. In this sense, chronic stress has been reported to evoke neuroplasticity in corticotropin-releasing factor (CRF) neurotransmission in several limbic structures, including the bed nucleus of the stria terminalis. However, a possible involvement of BNST CRF neurotransmission in cardiovascular dysfunctions evoked by chronic stress has never been reported. Thus, this study investigated the involvement of CRF₁ and CRF₂ receptors within the BNST in cardiovascular changes evoked by chronic stress in rats. We identified that exposure to a 10-day chronic variable stress (CVS) protocol decreased expression of both CRF₁ and CRF₂ receptors within the BNST. These effects were followed by increased arterial pressure and impairment of baroreflex function, but without changes on heart rate. Bilateral microinjection of either the selective CRF₁ receptor antagonist CP376395 or the selective CRF₂ receptor antagonist antisauvagine-30 into the BNST did not affect CVS-evoked arterial pressure increase. Nevertheless, BNST treatment with CP376395 decreased both tachycardic and bradycardic responses of the baroreflex in non-stressed rats; but these effects were not identified in chronically stressed animals. BNST pharmacological treatment with antisauvagine-30 decreased the reflex tachycardia in control animals, whereas reflex bradycardic response was increased in CVS animals. Altogether, the results reported in the present study indicate that down regulation of both CRF₁ and CRF₂ receptors within the BNST is involved in baroreflex impairment evoked by chronic stress.

RNA editing of the 5-HT2C receptor in the central nucleus of the amygdala is involved in resilience behavior

Post-traumatic-stress-disorder (PTSD) is a stress-related condition that may develop after exposure to a severe trauma-event. One of the core brain areas that is considered to be a key regulatory region of PTSD is the amygdala. Specifically, the central amygdala (CeA) is involved in emotion processing and associative fear learning memory, two main circuits involved in PTSD. Long term dysregulation of trauma-related emotional processing may be caused by neuroadaptations that affect gene expression. The adenosine-(A) to-inosine (I) RNA editing machinery is a post-transcriptional process that converts a genomic encoded A to I and is critical for normal brain function and development. Such editing has the potential to increase the transcriptome diversity, and disruption of this process has been linked to various central nervous system disorders. Here, we employed a unique animal model to examine the possibility that the RNA editing machinery is involved in PTSD. Detection of RNA editing specifically in the CeA revealed changes in the editing pattern of the 5-HT2C serotonin receptor (5-HT2CR) transcript accompanied by dynamic changes in the expression levels of the ADAR family enzymes (ADAR and ADARb1). Deamination by ADAR and ADARb1 enzymes induces conformational changes in the 5-HT2CR that decrease the G-protein-coupling activity, agonist affinity, and thus serotonin signaling. Significantly, a single intra-CeA administration of a 5-HT2CR pharmacological antagonist produced a robust alleviation of PTSD-like behaviors (that was maintained for three weeks) as well as single systemic treatment. This work may suggest the way to a new avenue in the understanding of PTSD regulation.

The bed nucleus of the stria terminalis and functionally linked neurocircuitry modulate emotion processing and HPA axis dysfunction in posttraumatic stress disorder

•

Task-based functional cooccurrence (tbFC) elucidates role of BNST in human PTSD neurocircuitry.

•

The BNST is hyperactive during the processing of trauma-related words in PTSD.

•

BNST activity correlates to PTSD symptom severity and reduced diurnal cortisol index.

•

The BNST has positive tbFC with negative emotion- and stress-related neurocircuitry.

•

The BNST has negative tbFC with executive function and stress regulation neurocircuitry.

Background

The bed nucleus of the stria terminalis (BNST) plays an important role in rodent posttraumatic stress disorder (PTSD), but evidence to support its relevance to human PTSD is limited. We sought to understand the role of the BNST in human PTSD via fMRI, behavioral, and physiological measurements.

Methods

29 patients with PTSD (childhood sexual abuse) and 23 healthy controls (HC) underwent BOLD imaging with an emotional word paradigm. Symptom severity was assessed using the Clinician-Administered PTSD Scale and HPA-axis dysfunction was assessed by measuring the diurnal cortisol amplitude index (DCAI). A data-driven multivariate analysis was used to determine BNST task-based functional co-occurrence (tbFC) across individuals.

Results

In the trauma-versus-neutral word contrast, patients showed increased activation compared to HC in the BNST, medial prefrontal cortex (mPFC), posterior cingulate gyrus (PCG), caudate heads, and midbrain, and decreased activation in dorsolateral prefrontal cortex (DLPFC). Symptom severity positively correlated with activity in the BNST, caudate head, amygdala, hippocampus, dorsal anterior cingulate gyrus (dACG), and PCG, and negatively with activity in the medial orbiotofrontal cortex (mOFC) and DLPFC. Patients and HC showed marked differences in the relationship between the DCAI and BOLD activity in the BNST, septal nuclei, dACG, and PCG. Patients showed stronger tbFC between the BNST and closely linked limbic and subcortical regions, and a loss of negative tbFC between the BNST and DLPFC.

Conclusions

Based upon novel data, we present a new model of dysexecutive emotion processing and HPA-axis dysfunction in human PTSD that incorporates the role of the BNST and functionally linked neurocircuitry.

Network Neuromodulation of Opioid and GABAergic Receptors Following a Combination of "Juvenile" and "Adult Stress" in Rats

Early life stress is suggested to alter behavioral responses during stressful challenges in adulthood and to exacerbate pathological symptoms that reminisce posttraumatic stress disorder (PTSD). These effects are often associated with changes in γ-Aminobutyric acid type A (GABAA) and κ opioid receptor expression and neuromodulation of the limbic system. Anxiety-like and stress coping behaviors were assessed in rats exposed to stress in adulthood on the background of previous exposure to stress in juvenility. Two weeks following behavioral assessment in adulthood, GABAAR α1 and α2 subunits and κ opioid receptor expression levels were measured in the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), amygdala, and periaqueductal gray (PAG). To illustrate changes at the network level, an integrated expression profile was constructed. We found that exposure to juvenile stress affected rats’ behavior during adult stress. The combination of juvenile and adult stress significantly affected rats’ long term anxious-like behavior. Probabilities predicting model integrating the expression of GABAA α1-α2 and κ opioid receptors in different brain regions yielded highly successful classification rates. This study emphasizes the ability of exposure to stress in juvenility to exacerbate the impact of coping with stress in adulthood. Moreover, the use of integrated receptor expression network profiling was found to effectively characterize the discussed affective styles and their behavioral manifestations.

Cannabinoids as therapeutics for PTSD

Post-traumatic stress disorder (PTSD) is a complex disorder that involves dysregulation of multiple neurobiological systems. The traumatic stressor plays a causal role in producing psychological dysfunction and the pattern of findings suggests that the hypothalamic-pituitary-adrenal (HPA) axis, which is instrumental for stress adaptation, is critically dysfunctional in PTSD. Given the lack of understanding of the basic mechanisms and underlying pathways that cause the disorder and its heterogeneity, PTSD poses challenges for treatment. Targeting the endocannabinoid (ECB) system to treat mental disorders, and PTSD in particular, has been the focus of research and interest in recent years. The ECB system modulates multiple functions, and drugs enhancing ECB signaling have shown promise as potential therapeutic agents in stress effects and other psychiatric and medical conditions. In this review, we focus on the interaction between the ECB-HPA systems in animal models for PTSD and in patients with PTSD. We summarize evidence supporting the use of cannabinoids in preventing and treating PTSD in preclinical and clinical studies. As the HPA system plays a key role in the mediation of the stress response and the pathophysiology of PTSD, we describe preclinical studies suggesting that enhancing ECB signaling is consistent with decreasing PTSD symptoms and dysfunction of the HPA axis. Overall, we suggest that a pharmacological treatment targeted at one system (e.g., HPA) may not be very effective because of the heterogeneity of the disorder. There are abnormalities across different neurotransmitter systems in the pathophysiology of PTSD and none of these systems function uniformly among all patients with PTSD. Hence, conceptually, enhancing ECB signaling may be a more effective avenue for pharmacological treatment.

Susceptibility and Resilience to PTSD-Like Symptoms in Mice Are Associated with Opposite Dendritic Changes in the Prelimbic and Infralimbic Cortices Following Trauma

Post-traumatic stress disorder (PTSD) is triggered by exposure to traumatic events, but not everyone who experiences trauma develops this disorder. Like humans, PTSD-like symptoms develop in some laboratory rodents (susceptible individuals), while others express less or no symptoms (resilient individuals). Here, considering (i) the putative causal role of fear conditioning in PTSD development and (ii) the involvement of the medial prefrontal cortex (mPFC) in the regulation of conditioned fear response, we tested whether trauma-associated changes in the mPFC may discriminate stress-resilient from stress-susceptible mice. From data on avoidance behavior (as a major symptom), we found that trauma-exposed mice displayed a bimodal distribution in their step-through latency, with low avoider (stress-resilient) individuals and high avoider (stress-susceptible) individuals. Dendrites of Golgi-Cox-stained neurons were analyzed in two parts of the mPFC: the prelimbic (PrL) and infralimbic (IL) areas. In the resilient phenotype, the total number of dendrites decreased in the PrL and increased in the IL; however, it decreased only in the IL in the susceptible phenotype compared to controls. These findings demonstrate that the type of post-trauma morphological changes in the mPFC is associated with susceptibility or resilience to trauma-related symptoms.

Animal Models of PTSD: A Critical Review

The goals of animal research in post-traumatic stress disorder (PTSD) include better understanding the neurophysiological etiology of PTSD, identifying potential targets for novel pharmacotherapies, and screening drugs for their potential use as PTSD treatment in humans. Diagnosis of PTSD relies on a patient interview and, as evidenced by changes to the diagnostic criteria in the DSM-5, an adequate description of this disorder in humans is a moving target. Therefore, it may seem insurmountable to model the construct of PTSD in animals such as rodents. Fortunately, the neural circuitry involved in fear and anxiety, thought to be essential to the etiology of PTSD in humans, is highly conserved throughout evolution. Furthermore, many symptoms can be modeled using behavioral tests that have face, construct, and predictive validity. Because PTSD is precipitated by a definite traumatic experience, animal models can simulate the induction of PTSD, and test causal factors with longitudinal designs. Accordingly, several animal models of physical and psychological trauma have been established. This review discusses the widely used animal models of PTSD in rodents, and overviews their strengths and weaknesses in terms of face, construct, and predictive validity.

Role of the Bed Nucleus of the Stria Terminalis in PTSD: Insights From Preclinical Models

Post-traumatic stress disorder (PTSD) afflicts approximately 8% of the United States population and represents a significant public health burden, but the underlying neural mechanisms of this and other anxiety- and stressor-related disorders are largely unknown. Within the last few decades, several preclinical models of PSTD have been developed to help elucidate the mechanisms underlying dysregulated fear states. One brain area that has emerged as a critical mediator of stress-related behavioral processing in both clinical and laboratory settings is the bed nucleus of the stria terminalis (BNST). The BNST is interconnected with essential emotional processing regions, including prefrontal cortex, hippocampus and amygdala. It is activated by stressor exposure and undergoes neurochemical and morphological alterations as a result of stressor exposure. Stress-related neuro-peptides including corticotropin-releasing factor (CRF) and pituitary adenylate cyclase activating peptide (PACAP) are also abundant in the BNST, further implicating an involvement of BNST in stress responses. Behaviorally, the BNST is critical for acquisition and expression of fear and is well positioned to regulate fear relapse after periods of extinction. Here, we consider the role of the BNST in stress and memory processes in the context of preclinical models of PTSD.

Animal models of PTSD: a challenge to be met

Recent years have seen increased interest in psychopathologies related to trauma exposure. Specifically, there has been a growing awareness to posttraumatic stress disorder (PTSD) in part due to terrorism, climate change-associated natural disasters, the global refugee crisis, and increased violence in overpopulated urban areas. However, notwithstanding the increased awareness to the disorder, the increasing number of patients, and the devastating impact on the lives of patients and their families, the efficacy of available treatments remains limited and highly unsatisfactory. A major scientific effort is therefore devoted to unravel the neural mechanisms underlying PTSD with the aim of paving the way to developing novel or improved treatment approaches and drugs to treat PTSD. One of the major scientific tools used to gain insight into understanding physiological and neuronal mechanisms underlying diseases and for treatment development is the use of animal models of human diseases. While much progress has been made using these models in understanding mechanisms of conditioned fear and fear memory, the gained knowledge has not yet led to better treatment options for PTSD patients. This poor translational outcome has already led some scientists and pharmaceutical companies, who do not in general hold opinions against animal models, to propose that those models should be abandoned. Here, we critically examine aspects of animal models of PTSD that may have contributed to the relative lack of translatability, including the focus on the exposure to trauma, overlooking individual and sex differences, and the contribution of risk factors. Based on findings from recent years, we propose research-based modifications that we believe are required in order to overcome some of the shortcomings of previous practice. These modifications include the usage of animal models of PTSD which incorporate risk factors and of the behavioral profiling analysis of individuals in a sample. These modifications are aimed to address factors such as individual predisposition and resilience, thus taking into consideration the fact that only a fraction of individuals exposed to trauma develop PTSD. We suggest that with an appropriate shift of practice, animal models are not only a valuable tool to enhance our understanding of fear and memory processes, but could serve as effective platforms for understanding PTSD, for PTSD drug development and drug testing.

The CRF Family of Neuropeptides and their Receptors - Mediators of the Central Stress Response

Background:

Dysregulated stress neurocircuits, caused by genetic and/or environmental changes, underlie the development of many neuropsychiatric disorders. Corticotropin-releasing factor (CRF) is the major physiological activator of the hypothalamic-pituitary-adrenal (HPA) axis and conse-quently a primary regulator of the mammalian stress response. Together with its three family members, urocortins (UCNs) 1, 2, and 3, CRF integrates the neuroendocrine, autonomic, metabolic and behavioral responses to stress by activating its cognate receptors CRFR1 and CRFR2.

Objective:

Here we review the past and current state of the CRF/CRFR field, ranging from pharmacologi-cal studies to genetic mouse models and virus-mediated manipulations.

Results:

Although it is well established that CRF/CRFR1 signaling mediates aversive responses, includ-ing anxiety and depression-like behaviors, a number of recent studies have challenged this viewpoint by revealing anxiolytic and appetitive properties of specific CRF/CRFR1 circuits. In contrast, the UCN/CRFR2 system is less well understood and may possibly also exert divergent functions on physiol-ogy and behavior depending on the brain region, underlying circuit, and/or experienced stress conditions.

Conclusion:

A plethora of available genetic tools, including conventional and conditional mouse mutants targeting CRF system components, has greatly advanced our understanding about the endogenous mecha-nisms underlying HPA system regulation and CRF/UCN-related neuronal circuits involved in stress-related behaviors. Yet, the detailed pathways and molecular mechanisms by which the CRF/UCN-system translates negative or positive stimuli into the final, integrated biological response are not completely un-derstood. The utilization of future complementary methodologies, such as cell-type specific Cre-driver lines, viral and optogenetic tools will help to further dissect the function of genetically defined CRF/UCN neurocircuits in the context of adaptive and maladaptive stress responses.

Effects of Trauma in Adulthood and Adolescence on Fear Extinction and Extinction Retention: Advancing Animal Models of Posttraumatic Stress Disorder

Evidence for and against adolescent vulnerability to posttraumatic stress disorder (PTSD) is mounting, but this evidence is largely qualitative, retrospective, or complicated by variation in prior stress exposure and trauma context. Here, we examine the effects of development on trauma vulnerability using adult post-natal (PN) day 61, early adolescent (PN23) and mid adolescence (PN34) rats and two types of trauma: an established animal model of PTSD, single prolonged stress (SPS), and a novel composite model—SPS predation (SPSp) version. We demonstrate that early and mid adolescent rats are capable of fear conditioning and fear extinction, as well as extinction retention. Our results also demonstrate that both types of trauma induced a deficit in the retention of fear extinction in adulthood, a hallmark of PTSD, but not after early or mid adolescence trauma, suggesting that adolescence might convey resilience to SPS and SPSp traumas. Across all three life stages, the effects of SPS exposure and a novel predation trauma model, SPSp, had similar effects on behavior suggesting that trauma type did not affect the likelihood of developing PTSD-like symptoms, and that SPSp is a predation-based trauma model worth exploring.

The Corticotropin-Releasing Factor Family: Physiology of the Stress Response

The physiological stress response is responsible for the maintenance of homeostasis in the presence of real or perceived challenges. In this function, the brain activates adaptive responses that involve numerous neural circuits and effector molecules to adapt to the current and future demands. A maladaptive stress response has been linked to the etiology of a variety of disorders, such as anxiety and mood disorders, eating disorders, and the metabolic syndrome. The neuropeptide corticotropin-releasing factor (CRF) and its relatives, the urocortins 1–3, in concert with their receptors (CRFR1, CRFR2), have emerged as central components of the physiological stress response. This central peptidergic system impinges on a broad spectrum of physiological processes that are the basis for successful adaptation and concomitantly integrate autonomic, neuroendocrine, and behavioral stress responses. This review focuses on the physiology of CRF-related peptides and their cognate receptors with the aim of providing a comprehensive up-to-date overview of the field. We describe the major molecular features covering aspects of gene expression and regulation, structural properties, and molecular interactions, as well as mechanisms of signal transduction and their surveillance. In addition, we discuss the large body of published experimental studies focusing on state-of-the-art genetic approaches with high temporal and spatial precision, which collectively aimed to dissect the contribution of CRF-related ligands and receptors to different levels of the stress response. We discuss the controversies in the field and unravel knowledge gaps that might pave the way for future research directions and open up novel opportunities for therapeutic intervention.

Sex-Dependent Effects of Mild Blast-induced Traumatic Brain Injury on Corticotropin-releasing Factor Receptor Gene Expression: Potential Link to Anxiety-like Behaviors

Traumatic brain injury (TBI) affects 1.7 million people in the United States every year, resulting in increased risk of death and disabilities. A significant portion of TBIs experienced by military personnel are induced by explosive blast devices. Active duty military personnel are especially vulnerable to mild blast-induced (mb)TBI and the associated long-term effects, such as anxiety disorders. Additionally, females are at an increased risk of being diagnosed with anxiety-related disorders. The mechanism by which mbTBI results in anxiety disorders in males and females is unknown. The sexually dimorphic corticotropin-releasing factor (CRF) is a brain signaling system linked to anxiety. CRF and its family of related peptides modulate anxiety-related behaviors by binding to CRF receptor subtypes 1 and 2 (CRFR1, CRFR2, respectively). These receptors are distributed throughout limbic structures that control behaviors related to emotion, memory, and arousal. Therefore, the aim of this study was to understand the link between mbTBI and anxiety by examining the impact of mbTBI on the CRFR system in male and female mice. mbTBI increased anxiety-like behaviors in both males and females (p < 0.05). In the present study, mbTBI did not alter CRFR1 gene expression in males or females. However, mbTBI disrupted CRFR2 gene expression in different limbic structures in males and females. In males, mbTBI increased baseline CRFR2 gene expression in the ventral hippocampus (p < 0.05) and decreased restraint-induced expression in the anterior bed nucleus of the stria terminalis (aBNST) and amygdala (p < 0.05). In females, mbTBI decreased restraint-induced CRFR2 gene expression in the dorsal hippocampus (p < 0.05). The inherent sex differences and the mbTBI-induced decrease in restraint-induced CRFR2 gene expression may contribute to anxiety-like behaviors. The results of the present study show that the response to mbTBI within the limbic structures modulates anxiety in a sex-dependent manner. The studies further suggest that CRFR2 may serve as a potential target to mitigate mbTBI effects.

Current Status of Animal Models of Posttraumatic Stress Disorder: Behavioral and Biological Phenotypes, and Future Challenges in Improving Translation

Increasing predictability of animal models of posttraumatic stress disorder (PTSD) has required active collaboration between clinical and preclinical scientists. Modeling PTSD is challenging, as it is a heterogeneous disorder with ≥20 symptoms. Clinical research increasingly utilizes objective biological measures (e.g., imaging, peripheral biomarkers) or nonverbal behaviors and/or physiological responses to complement verbally reported symptoms. This shift toward more-objectively measurable phenotypes enables refinement of current animal models of PTSD, and it supports the incorporation of homologous measures across species. We reviewed >600 articles to examine the ability of current rodent models to probe biological phenotypes of PTSD (e.g., sleep disturbances, hippocampal and fear-circuit dysfunction, inflammation, glucocorticoid receptor hypersensitivity) in addition to behavioral phenotypes. Most models reliably produced enduring generalized anxiety-like or depression-like behaviors, as well as hyperactive fear circuits, glucocorticoid receptor hypersensitivity, and response to long-term selective serotonin reuptake inhibitors. Although a few paradigms probed fear conditioning/extinction or utilized peripheral immune, sleep, and noninvasive imaging measures, we argue that these should be incorporated more to enhance translation. Data on female subjects, on subjects at different ages across the life span, or on temporal trajectories of phenotypes after stress that can inform model validity and treatment study design are needed. Overall, preclinical (and clinical) PTSD researchers are increasingly incorporating homologous biological measures to assess markers of risk, response, and treatment outcome. This shift is exciting, as we and many others hope it not only will support translation of drug efficacy from animal models to clinical trials but also will potentially improve predictability of stage II for stage III clinical trials.

Corticotropin-Releasing Factor Receptors Modulate Oxytocin Release in the Dorsolateral Bed Nucleus of the Stria Terminalis (BNST) in Male Rats

The neuropeptide oxytocin (OT) plays an important role in the regulation of social and anxiety-like behavior. Our previous studies have shown that OT neurons send projections from the hypothalamus to the dorsolateral bed nucleus of the stria terminalis (BNST_dl), a forebrain region critically involved in the modulation of anxiety-like behavior. Importantly, these OT terminals in the BNST_dl express presynaptic corticotropin releasing factor (CRF) receptor type 2 (CRFR2). This suggests that CRFR2 might be involved in the modulation of OT release. To test this hypothesis, we measured OT content in microdialysates collected from the BNST_dl of freely-moving male Sprague-Dawley rats following the administration of a selective CRFR2 agonist (Urocortin 3) or antagonist (Astressin 2B, As2B). To determine if type 1 CRF receptors (CRFR1) are also involved, we used selective CRFR1 antagonist (NBI35965) as well as CRF, a putative ligand of both CRFR1 and CRFR2. All compounds were delivered directly into the BNST_dl via reverse dialysis. OT content in the microdialysates was measured with highly sensitive and selective radioimmunoassay. Blocking CRFR2 with As2B caused an increase in OT content in BNST_dl microdialysates, whereas CRFR2 activation by Urocortin 3 did not have an effect. The As2B-induced increase in OT release was blocked by application of the CRFR1 antagonist demonstrating that the effect was dependent on CRFR1 transmission. Interestingly, CRF alone caused a delayed increase in OT content in BNST_dl microdialysates, which was dependent on CRF2 but not CRF1 receptors. Our results suggest that members of the CRF peptide family modulate OT release in the BNST_dl via a fine-tuned mechanism that involves both CRFR1 and CRFR2. Further exploration of mechanisms by which endogenous OT system is modulated by CRF peptide family is needed to better understand the role of these neuropeptides in the regulation of anxiety and the stress response.

Similar effect of CRF1 and CRF2 receptor in the basolateral or central nuclei of the amygdala on tonic immobility behavior

Studies have used paradigms based on animal models to understand human emotional behavior because they appear to be correlated with fear- and anxiety-related defensive patterns in non-human mammals. In this context, tonic immobility (TI) behavior is an innate response associated with extreme threat situations, such as predator attack. Some reports have demonstrated the involvement of corticotropin-releasing factor (CRF) in regulation of the endocrine system, defensive behaviors and behavioral responses to stress. Particularly, a previous study showed that the activation of CRF receptors in the basolateral (BLA) or central (CeA) nuclei of the amygdala increased TI responses, whereas treatment with a non-selective CRF antagonist, alpha-helical-CRF_9-41, decreased this innate fear response. However, while CRF₁ receptors have pronounced effects in stress-induced anxiety, CRF₂ receptors appear be involved in the expression of both stress-induced anxiety and spontaneous anxiety behavior. In this study, we investigated the effects of specific CRF receptors, CRF₁ and CRF₂, in the BLA and CeA on the duration of TI in guinea pigs. The results show that blockade of CRF₁ and CRF₂ receptors in the BLA and CeA produces a decrease in fear and/or anxiety, as suggested by a decrease in TI duration in the guinea pigs. Additionally, the specific antagonists for CRF₁ and CRF₂ receptors were able to prevent the increase in TI duration induced by CRF administration at the same sites. These results suggest that the modulation of fear and anxiety by the CRF system in the BLA and CeA occurs through concomitant effects on CRF₁ and CRF₂ receptors.

CRF receptor type 2 neurons in the posterior bed nucleus of the stria terminalis critically contribute to stress recovery

The bed nucleus of the stria terminalis (BNST) is critical in mediating states of anxiety, and its dysfunction has been linked to stress-related mental disease. Although the anxiety-related role of distinct subregions of the anterior BNST was recently reported, little is known about the contribution of the posterior BNST (pBNST) to the behavioral and neuroendocrine responses to stress. Previously, we observed abnormal expression of corticotropin-releasing factor receptor type 2 (CRFR2) to be associated with post-traumatic stress disorder (PTSD)-like symptoms. Here, we found that CRFR2-expressing neurons within the pBNST send dense inhibitory projections to other stress-related brain regions (for example, the locus coeruleus, medial amygdala and paraventricular nucleus), implicating a prominent role of these neurons in orchestrating the neuroendocrine, autonomic and behavioral response to stressful situations. Local CRFR2 activation by urocortin 3 depolarized the cells, increased the neuronal input resistance and increased firing of action potentials, indicating an enhanced excitability. Furthermore, we showed that CRFR2-expressing neurons within the pBNST are critically involved in the modulation of the behavioral and neuroendocrine response to stress. Optogenetic activation of CRFR2 neurons in the pBNST decreased anxiety, attenuated the neuroendocrine stress response, ameliorated stress-induced anxiety and impaired the fear memory for the stressful event. Moreover, activation following trauma exposure reduced the susceptibility for PTSD-like symptoms. Optogenetic inhibition of pBNST CRFR2 neurons yielded opposite effects. These data indicate the relevance of pBNST activity for adaptive stress recovery.

The Corticotropin Releasing Factor Receptor 1 in Alcohol Use Disorder: Still a Valid Drug Target?

Corticotropin releasing factor (CRF) is a neuropeptide that plays a key role in behavioral and physiological responses to stress. A large body of animal literature implicates CRF acting at type 1 CRF receptors (CRFR1) in consumption by alcohol-dependent subjects, stress-induced reinstatement of alcohol seeking, and possibly binge alcohol consumption. These studies have encouraged recent pilot studies of CRFR1 antagonists in humans with alcohol use disorder (AUD). It was a great disappointment to many in the field that these studies failed to show an effect of these compounds on stress-induced alcohol craving. Here, we examine these studies to explore potential limitations and discuss preclinical and human literature to ask whether CRFR1 is still a valid drug target to pursue for the treatment of AUD.

Opiates Modulate Noxious Chemical Nociception through a Complex Monoaminergic/Peptidergic Cascade

The ability to detect noxious stimuli, process the nociceptive signal, and elicit an appropriate behavioral response is essential for survival. In Caenorhabditis elegans, opioid receptor agonists, such as morphine, mimic serotonin, and suppress the overall withdrawal from noxious stimuli through a pathway requiring the opioid-like receptor, NPR-17. This serotonin- or morphine-dependent modulation can be rescued in npr-17-null animals by the expression of npr-17 or a human κ opioid receptor in the two ASI sensory neurons, with ASI opioid signaling selectively inhibiting ASI neuropeptide release. Serotonergic modulation requires peptides encoded by both nlp-3 and nlp-24, and either nlp-3 or nlp-24 overexpression mimics morphine and suppresses withdrawal. Peptides encoded by nlp-3 act differentially, with only NLP-3.3 mimicking morphine, whereas other nlp-3 peptides antagonize NLP-3.3 modulation. Together, these results demonstrate that opiates modulate nociception in Caenorhabditis elegans through a complex monoaminergic/peptidergic cascade, and suggest that this model may be useful for dissecting opiate signaling in mammals.

SIGNIFICANCE STATEMENT

Opiates are used extensively to treat chronic pain. In Caenorhabditis elegans, opioid receptor agonists suppress the overall withdrawal from noxious chemical stimuli through a pathway requiring an opioid-like receptor and two distinct neuropeptide-encoding genes, with individual peptides from the same gene functioning antagonistically to modulate nociception. Endogenous opioid signaling functions as part of a complex, monoaminergic/peptidergic signaling cascade and appears to selectively inhibit neuropeptide release, mediated by a α-adrenergic-like receptor, from two sensory neurons. Importantly, receptor null animals can be rescued by the expression of the human κ opioid receptor, and injection of human opioid receptor ligands mimics exogenous opiates, highlighting the utility of this model for dissecting opiate signaling in mammals.

Abundant collateralization of temporal lobe projections to the accumbens, bed nucleus of stria terminalis, central amygdala and lateral septum

Behavioral flexibility is subserved in part by outputs from the cerebral cortex to telencephalic subcortical structures. In our earlier evaluation of the organization of the cortical-subcortical output system (Reynolds and Zahm, J Neurosci 25:11757-11767, 2005), retrograde double-labeling was evaluated in the prefrontal cortex following tracer injections into pairs of the following subcortical telencephalic structures: caudate-putamen, core and shell of the accumbens (Acb), bed nucleus of stria terminalis (BST) and central nucleus of the amygdala (CeA). The present study was done to assess patterns of retrograde labeling in the temporal lobe after similar paired tracer injections into most of the same telencephalic structures plus the lateral septum (LS). In contrast to the modest double-labeling observed in the prefrontal cortex in the previous study, up to 60-80 % of neurons in the basal and accessory basal amygdaloid nuclei and amygdalopiriform transition area exhibited double-labeling in the present study. The most abundant double-labeling was generated by paired injections into structures affiliated with the extended amygdala, including the CeA, BST and Acb shell. Injections pairing the Acb core with the BST or CeA produced significantly fewer double-labeled neurons. The ventral subiculum exhibited modest amounts of double-labeling associated with paired injections into the Acb, BST, CeA and LS. The results raise the issue of how an extraordinarily collateralized output from the temporal lobe may contribute to behavioral flexibility.

The CRF System as a Therapeutic Target for Neuropsychiatric Disorders

The major neuropsychiatric disorders are devastating illnesses that are only modestly responsive to treatment. Improving the treatment of these conditions will require innovative new strategies that depart from previously focused-on pharmacological mechanisms. Considerable preclinical and clinical data indicate corticotropin-releasing factor (CRF) signaling as a target for new psychotropic drug development. Here we review alterations in the CRF system reported in several psychiatric conditions. We also examine the preclinical work that has dissected the distinctive roles of CRF receptors in specific circuits relevant to these disorders. We further describe the clinical trials of CRF1 receptor antagonists that have been conducted. Although these clinical trials have thus far met with limited therapeutic success, the unfolding complexity of the CRF system promises many future directions for studying its role in the etiology and treatment of neuropsychiatric conditions.

The neurocircuitry of remote cued fear memory

Memories of threatening, fear-evoking events can persist even over a lifetime. While fear memory is widely considered to be a highly persistent and durable form of memory, its circuits are not. This article reviews the dynamic temporal representation of remote fear memory in the brain, at the level of local circuits and distributed networks. Data from the study of Pavlovian cued fear conditioning suggests memory retrieval remains amygdala-dependent, even over protracted time scales, all the while interconnected cortical and subcortical circuits are newly recruited and progressively reorganized. A deeper understanding into how the neurocircuitry of cued fear memory reorganizes with the passage of time will advance our ongoing search for the elusive physical changes representing fear memories in the brain. Considering that persistent, pathological fear memories are a hallmark feature of post-traumatic stress disorder (PTSD), the behavioral and circuit-level study of remote cued fear memory retrieval adds a key element towards a systems understanding of PTSD.

Region-specific roles of the corticotropin-releasing factor-urocortin system in stress

Dysregulation of the corticotropin-releasing factor (CRF)-urocortin (UCN) system has been implicated in stress-related psychopathologies such as depression and anxiety. It has been proposed that CRF-CRF receptor type 1 (CRFR1) signalling promotes the stress response and anxiety-like behaviour, whereas UCNs and CRFR2 activation mediate stress recovery and the restoration of homeostasis. Recent findings, however, provide clear evidence that this view is overly simplistic. Instead, a more complex picture has emerged that suggests that there are brain region- and cell type-specific effects of CRFR signalling that are influenced by the individual's prior experience and that shape molecular, cellular and ultimately behavioural responses to stressful challenges.

Overexpression of CRF in the BNST diminishes dysphoria but not anxiety-like behavior in nicotine withdrawing rats

Smoking cessation leads to dysphoria and anxiety, which both increase the risk for relapse. This negative affective state is partly mediated by an increase in activity in brain stress systems. Recent studies indicate that prolonged viral vector-mediated overexpression of stress peptides diminishes stress sensitivity. Here we investigated whether the overexpression of corticotropin-releasing factor (CRF) in the bed nucleus of the stria terminalis (BNST) diminishes nicotine withdrawal symptoms in rats. The effect of nicotine withdrawal on brain reward function was investigated with an intracranial self-stimulation (ICSS) procedure. Anxiety-like behavior was investigated in the elevated plus maze test and a large open field. An adeno-associated virus (AAV) pseudotype 2/5 vector was used to overexpress CRF in the lateral BNST and nicotine dependence was induced using minipumps. Administration of the nicotinic receptor antagonist mecamylamine and cessation of nicotine administration led to a dysphoria-like state, which was prevented by the overexpression of CRF in the BNST. Nicotine withdrawal also increased anxiety-like behavior in the elevated plus maze test and large open field test and slightly decreased locomotor activity in the open field. The overexpression of CRF in the BNST did not prevent the increase in anxiety-like behavior or decrease in locomotor activity. The overexpression of CRF increased CRF1 and CRF2 receptor gene expression and increased the CRF2/CRF1 receptor ratio. In conclusion, the overexpression of CRF in the BNST prevents the dysphoria-like state associated with nicotine withdrawal and increases the CRF2/CRF1 receptor ratio, which may diminish the negative effects of CRF on mood.

Overexpression of Forebrain CRH During Early Life Increases Trauma Susceptibility in Adulthood

Although early-life stress is a significant risk factor for developing anxiety disorders, including posttraumatic stress disorder (PTSD), the underlying mechanisms are unclear. Corticotropin releasing hormone (CRH) is disrupted in individuals with PTSD and early-life stress and hence may mediate the effects of early-life stress on PTSD risk. We hypothesized that CRH hyper-signaling in the forebrain during early development is sufficient to increase response to trauma in adulthood. To test this hypothesis, we induced transient, forebrain-specific, CRH overexpression during early-life (pre-puberty, CRHOEdev) in double-mutant mice (Camk2a-rtta2 × tetO-Crh) and tested their behavioral and gene expression responses to the predator stress model of PTSD in adulthood. In one cohort of CRHOEdev exposed and unexposed mice, avoidance and arousal behaviors were examined 7-15 days after exposure to predator stress. In another cohort, gene expression changes in Crhr1, Crhr2, and Fkbp51 in forebrain of CRHOEdev exposed and unexposed mice were examined 7 days after predator stress. CRHOEdev induced robust increases in startle reactivity and reductions in startle inhibition independently of predator stress in both male and female mice. Avoidance behaviors after predator stress were highly dependent on sex and CRHOEdev exposure. Whereas stressed females exhibited robust avoidance responses that were not altered by CRHOEdev, males developed significant avoidance only when exposed to both CRHOEdev and stress. Quantitative real-time-PCR analysis indicated that CRHOEdev unexposed males exhibit significant changes in Crhr2 expression in the amygdala and bed nucleus stria terminalis in response to stress, whereas males exposed to CRHOEdev did not. Similar to CRHOEdev males, females exhibited no significant Crhr2 gene expression changes in response to stress. Cortical Fkbp51 expression was also significantly reduced by stress and CRHOEdev exposure in males, but not in females. These findings indicate that forebrain CRH hyper-signaling in early-life is sufficient to increase enduring effects of adult trauma and attenuate Crhr2 expression changes in response to stress in males. These data support growing evidence for significant sex differences in response to trauma, and support further study of CRHR2 as a candidate mechanism for PTSD risk.

Bi-directional effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on fear-related behavior and c-Fos expression after fear conditioning in rats

Pituitary adenylate cyclase-activating polypeptide (PACAP) is implicated in stress regulation and learning and memory. PACAP has neuromodulatory actions on brain structures within the limbic system that could contribute to its acute and persistent effects in animal models of stress and anxiety-like behavior. Here, male Sprague-Dawley rats were implanted with intracerebroventricular (ICV) cannula for infusion of PACAP-38 (0.5, 1, or 1.5 μg) or vehicle followed 30 min later by fear conditioning. Freezing was measured early (1, 4, and 7 days) or following a delay (7, 10, and 13 days) after conditioning. PACAP (1.5 μg) produced a bi-phasic response in freezing behavior across test days: relative to controls, PACAP-treated rats showed a reduction in freezing when tested 1 or 7 days after fear conditioning that evolved into a significant elevation in freezing by the third test session in the early, but not delayed, group. Corticosterone (CORT) levels were significantly elevated in PACAP-treated rats following fear conditioning, but not at the time of testing (Day 1). Brain c-Fos expression revealed PACAP-dependent alterations within, as well as outside of, areas typically implicated in fear conditioning. Our findings raise the possibility that PACAP disrupts fear memory consolidation by altering synaptic plasticity within neurocircuits normally responsible for encoding fear-related cues, producing a type of dissociation or peritraumatic amnesia often seen in people early after exposure to a traumatic event. However, fear memories are retained such that repeated testing and memory reactivation (e.g., re-experiencing) causes the freezing response to emerge and persist at elevated levels. PACAP systems may represent an axis on which stress and exposure to trauma converge to promote maladaptive behavioral responses characteristic of psychiatric illnesses such as post-traumatic stress disorder (PTSD).

Animal models for posttraumatic stress disorder: An overview of what is used in research

Posttraumatic stress disorder (PTSD) is a common anxiety disorder characterised by its persistence of symptoms after a traumatic experience. Although some patients can be cured, many do not benefit enough from the psychological therapies or medication strategies used. Many researchers use animal models to learn more about the disorder and several models are available. The most-used physical stressor models are single-prolonged stress, restraint stress, foot shock, stress-enhanced fear learning, and underwater trauma. Common social stressors are housing instability, social instability, early-life stress, and social defeat. Psychological models are not as diverse and rely on controlled exposure to the test animal’s natural predator. While validation of these models has been resolved with replicated symptoms using analogous stressors, translating new findings to human patients remains essential for their impact on the field. Choosing a model to experiment with can be challenging; this overview of what is possible with individual models may aid in making a decision.

Incubation of Fear Is Regulated by TIP39 Peptide Signaling in the Medial Nucleus of the Amygdala

Fear-related psychopathologies such as post-traumatic stress disorder are characterized by impaired extinction of fearful memories. Recent behavioral evidence suggests that the neuropeptide tuberoinfundibular peptide of 39 residues (TIP39), via its receptor, the parathyroid hormone 2 receptor (PTH2R), modulates fear memory. Here we examined the anatomical and cellular localization of TIP39 signaling that contributes to the increase in fear memory over time following a traumatic event, called fear memory incubation. Contextual freezing, a behavioral sign of fear memory, was significantly greater in PTH2R knock-out than wild-type male mice 2 and 4 weeks after a 2 s 1.5 mA footshock. PTH2R knock-out mice had significantly reduced c-Fos activation in the medial amygdala (MeA) following both footshock and fear recall, but had normal activation in the hypothalamic paraventricular nucleus and the amygdalar central nucleus compared with wild-type. We therefore investigated the contribution of MeA TIP39 signaling to fear incubation. Similar to the effect of global TIP39 signaling loss, blockade of TIP39 signaling in the MeA by lentivirus-mediated expression of a secreted PTH2R antagonist augmented fear incubation. Ablation of MeA PTH2R-expressing neurons also strengthened the fear incubation effect. Using the designer receptor exclusively activated by designer drug pharmacogenetic approach, transient inhibition of MeA PTH2R-expressing neurons before or immediately after the footshock, but not at the time of fear recall, enhanced fear incubation. Collectively, the findings demonstrate that TIP39 signaling within the MeA at the time of an aversive event regulates the increase over time in fear associated with the event context.

SIGNIFICANCE STATEMENT

Fear-related psychopathologies such as post-traumatic stress disorder (PTSD) are characterized by excessive responses to trauma-associated cues. Fear responses can increase over time without additional cue exposure or stress. This work shows that modulatory processes within the medial nucleus of the amygdala near the time of a traumatic event influence the strength of fear responses that occur much later. The modulatory processes include signaling by the neuropeptide TIP39 and neurons that express its receptor. These findings will help in the understanding of why traumatic events sometimes have severe psychological consequences. One implication is that targeting neuromodulation in the medial amygdala could potentially help prevent development of PTSD.

Sex-specific neuroanatomical correlates of fear expression in prefrontal-amygdala circuits

BACKGROUND

The neural projections from the infralimbic region of the prefrontal cortex to the amygdala are important for the maintenance of conditioned fear extinction. Neurons in this pathway exhibit a unique pattern of structural plasticity that is sex-dependent, but the relationship between the morphologic characteristics of these neurons and successful extinction in male and female subjects is unknown.

METHODS

Using classic cued fear conditioning and an extinction paradigm in large cohorts of male and female rats, we identified subpopulations of both sexes that exhibited high (HF) or low (LF) levels of freezing on an extinction retrieval test, representing failed or successful extinction maintenance, respectively. We combined retrograde tracing with fluorescent intracellular microinjections to perform three-dimensional reconstructions of infralimbic neurons that project to the basolateral amygdala in these groups.

RESULTS

The HF and LF male rats exhibited neuroanatomical distinctions that were not observed in HF or LF female rats. A retrospective analysis of behavior during fear conditioning and extinction revealed that despite no overall sex differences in freezing behavior, HF and LF phenotypes emerged in male rats during extinction and in female rats during fear conditioning, which does not involve infralimbic-basolateral amygdala neurons.

CONCLUSIONS

Our results suggest that the neural processes underlying successful or failed extinction maintenance may be sex-specific. These findings are relevant not only to future basic research on sex differences in fear conditioning and extinction but also to exposure-based clinical therapies, which are similar in premise to fear extinction and which are primarily used to treat disorders that are more common in women than in men.

Pituitary adenylate cyclase activating polypeptide in stress-related disorders: data convergence from animal and human studies

The maladaptive expression and function of several stress-associated hormones have been implicated in pathological stress and anxiety-related disorders. Among these, recent evidence has suggested that pituitary adenylate cyclase activating polypeptide (PACAP) has critical roles in central neurocircuits mediating stress-related emotional behaviors. We describe the PACAPergic systems, the data implicating PACAP in stress biology, and how altered PACAP expression and signaling may result in psychopathologies. We include our work implicating PACAP signaling within the bed nucleus of the stria terminalis in mediating the consequences of stressor exposure and relatedly, describe more recent studies suggesting that PACAP in the central nucleus of the amygdala may impact the emotional aspects of chronic pain states. In aggregate, these results are consistent with data suggesting that PACAP dysregulation is associated with posttraumatic stress disorder in humans.

Neuropeptide regulation of signaling and behavior in the BNST

Recent technical developments have transformed how neuroscientists can probe brain function. What was once thought to be difficult and perhaps impossible, stimulating a single set of long range inputs among many, is now relatively straight-forward using optogenetic approaches. This has provided an avalanche of data demonstrating causal roles for circuits in a variety of behaviors. However, despite the critical role that neuropeptide signaling plays in the regulation of behavior and physiology of the brain, there have been remarkably few studies demonstrating how peptide release is causally linked to behaviors. This is likely due to both the different time scale by which peptides act on and the modulatory nature of their actions. For example, while glutamate release can effectively transmit information between synapses in milliseconds, peptide release is potentially slower [See the excellent review by Van Den Pol on the time scales and mechanisms of release (van den Pol, 2012)] and it can only tune the existing signals via modulation. And while there have been some studies exploring mechanisms of release, it is still not as clearly known what is required for efficient peptide release. Furthermore, this analysis could be complicated by the fact that there are multiple peptides released, some of which may act in contrast. Despite these limitations, there are a number of groups making progress in this area. The goal of this review is to explore the role of peptide signaling in one specific structure, the bed nucleus of the stria terminalis, that has proven to be a fertile ground for peptide action.

Central CRF2 receptor antagonism reduces anxiety states during amphetamine withdrawal

Increased depressive and anxiety-like behaviors are exhibited by rats and humans during withdrawal from psychostimulants. Anxiety-like behaviors observed during amphetamine withdrawal are mediated by increased expression and activity of corticotropin releasing factor type 2 (CRF2) receptors in the dorsal raphe nucleus (dRN). Anxiety-like behavior of rats during withdrawal can be reversed by CRF2 receptor antagonism in the dRN, but the efficacy of global central CRF2 receptor antagonism is unknown. Rats were treated with amphetamine (2.5mg/kg, ip.) or saline daily for 2 weeks, and were tested for anxiety-like behaviors during withdrawal. Rats undergoing withdrawal showed increased anxiety-like behavior, which was reduced by ventricular infusion of the CRF2 antagonist antisauvagine-30 (ASV 2 μg/2 μl). Surprisingly, ventricular ASV increased anxiety-like behavior in rats pre-treated with saline, but had an anxiolytic effect in un-treated rats. Western blots were performed to determine whether differences in CRF receptor densities could explain ASV-induced behavioral results. Saline pre-treated rats showed reduced CRF1 receptor expression in the lateral septum compared to amphetamine pre-treated and un-treated rats. Overall, these results suggest that central CRF2 antagonism reduces anxiety states during amphetamine withdrawal, and that behavioral effects may be dependent upon the balance of CRF1 and CRF2 receptor activity in anxiety-related regions.

Trauma-informed care: keeping mental health settings safe for veterans

Veterans, as military personnel returning from wars in Afghanistan and Iraq, are frequently coping with various mental health problems. These veterans are at high risk for posttraumatic stress disorder (PTSD) and associated behavioral consequences, including self-harm, verbal and physical aggression, and violence. In this article, we highlight the physiological, physical, and emotional consequences of trauma. We focus on the unique experiences that affect veterans' mental health and associated behaviors and advocate for veterans to receive evidenced-based treatment using trauma-informed and recovery-oriented care.